Plugging oil or gas wells with a cement plug is a common operation in the art. In general, one of the goals of plug cementing is to secure a stable and effective seal in a designated location of the wellbore. In other cases, a cement plug may be used to provide a base for initiating a derivation or kick-off when a directional change in drilling is desired.
Cement plugs are often constructed by pumping a cement slurry down a drill pipe. The pumped cement slurry then displaces a wellbore fluid such as a drilling fluid, and hardens forming a cement plug. Because a cement slurry is usually denser than a drilling fluid, the lighter drilling fluid tends to migrate upward and through the cement slurry. At the same time, the heavier cement slurry tends to fall in the wellbore as it sets up. This phenomenon is known as density swapping of fluids within the wellbore. Density swapping can ultimately lead to the plug failing to set in its intended place, and the subsequent mixing of wellbore fluids with the plug slurry can also have detrimental effects on the intended performance of the set cement.
Cement spacers can be used to aid separating drilling fluids from cement slurries. However, some known cement spacers are not entirely effective, and allow mixing and remixing of the fluids that they are designed to separate. Contamination of the cement slurries can slow or prevent setting or otherwise comprise the integrity of the cement plug. Accordingly, there remains a need in the art for alternative cement spacer fluids and methods of cementing a wellbore using the alternative cement spacer fluids.